I don't have any techniques for keeping myself motivated. What motivates me just happens... I can be struggling for days with one passage from Rouse's book and be ready to quit, but then one word finally makes sense and everything else becomes clearer. Ahhh, what a good feeling that is! Or else, I can finish a terribly difficult chapter without any good sensation, but then the next one proves to be a piece of cake. Ahhh, that's like paradise! Anywho, why don't you grab yourself an easy Greek reader and go over it once you finish a lesson you thought was particulary difficult: it will probably make your studies less boring.